In the field of optical communication which does not use optical guides/fibers in order to transmit the communication, several methods are known. These methods belong to several different sub-classes, usually referred to by different terms, such as Wireless/Fiberless Optical Communication (WOC/FOC, mainly used to describe indoors, short range systems), Free Space Optical Communication (FSO, mainly used to describe outdoors, mid/long range systems), Visible Light Communication (VLC, mainly used to describe indoors and outdoors, on the visible light spectrum).
It is estimated that for the same conditions of data rate, power, distances, angles, etc. optical communication is about ten times more efficient than RF communication. Usually, the quality, and therefore the efficiency of communication method is determined by measuring the Signal to Noise Ratio (SNR) provided by the method.
Although the optical communication is much more efficient than RF communication, both methods have a similar disadvantage in wide angle transmissions. Wide angle transmissions and receptions enable receiving the transmission over a large angular area and thus, for example, reduce the need for aiming the transmission, and enable roaming within the receiving area. However, for all methods which do not use guides, fibers or cables (both optical and RF) the energy and therefore the SNR are a result of the solid angle of transmission and the distance. In the transmitter side, the wider is the solid angle of transmission, the lower will be the energy flux; additionally, the flux drops proportionally to 1/r2, where r is the radius of the transmitted area. In the receiver side, the wider is the solid angle of reception, the larger is the background noise collected. As the SNR decreases (due to low energy or high noise), the ability to achieve high data rates for long distances may decrease also.
Usage of narrow angle transmissions and reception may reduce the above mentioned deficiencies. However, the possibilities in using narrow angle transmission or reception are very limited due to the directionality of the transmission. The narrow angle requires accurate detection and aiming of the transmission to the receiver, and therefore, for example, transmissions to mobile receivers (or from mobile transmitters) may be hard to apply.
Another known sub-class of methods includes usage of angular diversity and/or spatial multiplexing, which usually employ multiple transmitters and/or multiple receivers. These methods may provide some more operational freedom relative to regular narrow angle transmissions. However, these methods may still require scanning of the space for detection of the required receiver/transmitter, may support only point to point (one-on-one) communication and may suffer from several disconnections in case the receiver and or transmitter are in relative movement